The present invention relates to an apparatus and method of ion beam processing, and more specifically to an apparatus and method of ion beam processing suitable for processing silicon substrates by ion beam milling and ion beam sputtering.
As an ion beam processing apparatus, there is a well-known ion beam processing apparatus comprising an ion source for generating plasma by introducing Ar gas, etc., a processing chamber for holding a substrate in a vacuum atmosphere and processing the substrate with an ion beam, an ion source power supply for extracting the plasma generated by the ion source as an ion beam into an ion beam guide tube which connects the ion source with the processing chamber and then irradiating the ion beam on the substrate in the processing chamber, and a vacuum exhaust system for vacuum pumping the processing chamber.
Conventionally, this kind of ion beam processing apparatus provides a shutter plate being disposed so as to be freely opened and closed, between a substrate holder for holding a substrate and an ion source power supply, to prevent the ion beam extracted by the ion source power supply from being irradiated directly on the substrate before and after the milling process.
Further, when a substrate is processed by milling with the extracted ion beam, the surface of the substrate is positively charged due to the positive charge of the ion beam. For this reason, if the substrate surface remains charged in a positive state, electrostatic discharge damage (ESD) to elements is caused by charge-up on the substrate surface. To prevent this electrostatic discharge damage to the elements, an apparatus, called a neutralizer, is provided for supplying electrons between the ion source and the shutter plate.
As well-known neutralizers, there are a filament-type neutralizer which applies voltage to a filament to make it glow thereby releasing thermoelectrons, and a microwave neutralizer which guides a microwave between the ion source power supply and the shutter plate to generate plasma thereby supplying electrons from the generated plasma.
Incidentally, as the capacity of computer hard disks has become large lately, read/write magnetic heads have rapidly been microminiaturized and thin-film oriented. Elements used for magnetic heads are being shifted from MR (Magneto Resistive) heads to GMR (Giant Magneto Resistive) heads. In the future, it can be expected that the demand for larger capacity will shift the trend to more highly sensitive TMR (Tunnel Magneto Resistive) heads.
In a conventional ion beam processing apparatus, a quantitative balance between positively charged ion beams and negatively charged neutralizing electrons is not considered to be important. For this reason, as elements become microminiaturized and thin-film oriented, a problem of electrostatic discharge damage to the elements due to charge-up on the substrate surface becomes a more serious problem to be solved. Specifically, when the shutter plate is opened and closed, neutralizing electrons are drawn to the shutter plate as a result of the opening and closing action of the shutter plate. By doing so, the potential of the substrate surface becomes positively charged due to a lack of neutralization, thereby easily damaging the elements, which makes it difficult to process miniaturized, thin-film elements.
Therefore, this applicant has applied for a patent of a method for applying voltage to a shutter plate when the shutter plate is opened and closed so as to solve the problem of insufficient neutralization when the shutter plate is opened and closed (Patent Application No. 2000-260160). In this case, to solve the problem of insufficient neutralization when the shutter plate is opened and closed, a power supply is required to apply voltage to the shutter plate. Such an apparatus having the shutter plate is shown in Japanese Patent Application Laid-open No. 5-128997, for example.
The purpose of the present invention is to provide an apparatus and method of ion beam processing which can suppress rapid potential change on the surface of a process target when the shutter plate is opened and closed.
To solve said problem, the present invention constitutes an ion beam processing apparatus comprising an ion source for generating plasma by introducing gas; a processing chamber for processing a process target with an ion beam in a vacuum atmosphere; an ion source power supply for extracting the plasma generated by said ion source as an ion beam into an ion beam guide tube which connects said ion source with said processing chamber and then irradiating the ion beam on said process target in said processing chamber; a neutralizer for neutralizing said ion beam; a shutter plate, being disposed so as to be freely opened and closed at a location closer to said ion source side than said process target, for shielding said process target from said ion beam when it is closed; and ion beam control means for controlling the amount of ion beam extracted from said ion source power supply when said shutter plate is opened and closed.
When constituting said ion beam processing apparatus, instead of ion beam control means, it is possible to provide current quantity control means for controlling the quantity of ion beam current when the shutter plate is opened and closed, or voltage control means for controlling voltage of the ion source power supply when the shutter plate is opened and closed. In this case, it is preferable that the ion beam control means controls the amount of ion beam to decrease when the shutter plate is opened and closed, and that the current quantity control means controls the quantity of ion beam current to decrease when the shutter plate is opened and closed, and also that voltage control means controls the voltage to be low when the shutter plate is opened and closed.
Further, instead of using ion beam control means, current quantity control means, or voltage control means, it is also possible to control neutralization quantity of the neutralizer, for example, to control the neutralization ability to increase neutralization when the shutter plate is opened and closed. Furthermore, in addition to increasing the neutralization ability when the shutter plate is opened and closed, it is possible to simultaneously control the amount of ion beam to decrease or to control the ion source power supply voltage to become lower.
When constituting each of said ion beam processing apparatus, the following factors can be added.
(1) Said neutralizer is a filament-type neutralizer which emits thermoelectrons from the filament connected to the power supply and neutralizes said ion beam.
(2) Said neutralizer is a microwave neutralizer which generates plasma by irradiating a microwave into a magnetic field and neutralizes said ion beam by electrons contained in the generated plasma.
Further, the present invention can process a process target with an ion beam and-also, the following processing methods are available when said ion beam is neutralized.
(1) A method for shielding said process target with a shutter plate before and after the processing of said process target so as to block said ion beam from being irradiated on said process target; limiting the amount of said ion beam irradiated on said process target while retracting said shutter plate from the said ion beam irradiation area to the outside thereof or moving said shutter plate from the outside of the said ion beam irradiation area to the inside thereof in the process of starting or finishing processing said process target; and releasing the limitation to said ion beam and irradiating the ion beam on said process target during the processing after said shutter plate has been retracted outside the said ion beam irradiation area.
(2) A method for shielding said process target with a shutter plate before and after the processing of said process target so as to block said ion beam from being irradiated on said process target; limiting the amount of said ion beam irradiated on said process target in the process of moving said shutter plate inside and outside the said ion beam irradiation area; and then releasing the limitation to said ion beam and irradiating the ion beam on said process target during the processing after said shutter plate has been retracted outside the said ion beam irradiation area.
(3) A method for shielding said process target with a shutter plate before and after the processing of said process target so as to block said ion beam from being irradiated on said process target; increasing the ability to neutralize said ion beam in the process of moving said shutter plate inside and outside the said ion beam irradiation area; and irradiating said ion beam on said process target during the processing after said shutter plate has been retracted outside the said ion beam irradiation area while restoring said neutralization ability to the level used for the processing.
Because said means control the amount of ion beam, quantity of ion beam current, ion source power supply voltage, or neutralization quantity when the shutter plate is opened and closed, even if a quantitative balance between positively charged ion beams and negatively charged neutralizing electrons is lost when the shutter plate is opened and closed, it is possible to suppress quick potential change (charge-up) on the surface of the process target when the shutter plate is opened and closed, thereby suppressing the electrostatic discharge damage to the process target (element), thus making it possible to process a microminiaturized, thin-film element.
Further, because said means limit the amount of said ion beam irradiated on said process target while retracting said shutter plate from the said ion beam irradiation area to the outside thereof or moving said shutter plate from the outside of the said ion beam irradiation area to the inside thereof in the process of starting or finishing processing said process target; limit the amount of said ion beam irradiated on said process target in the process of moving said shutter plate inside and outside the said ion beam irradiation area; or increase the ability to neutralize said ion beam; even if a quantitative balance between positively charged ion beams and negatively charged neutralizing electrons is lost when the shutter plate is opened and closed, it is possible to suppress quick potential change (charge-up) on the surface of the process target when the shutter plate is opened and closed, thereby suppressing the electrostatic discharge damage to the process target (element), thus making it possible to process a microminiaturized, thin-film element.